(a) Field of the Invention
The present invention relates to a converter and, more particularly, to a converter which can discharge molten metal to a suitable place free from slag.
(b) Description of the Related Art
Generally, molten pig iron passed through hot metal pretreatment process such as de-phosphorization and de-sulphurization is charged into a converter together with other materials including main components such as scrap and cold iron, and subsidiary components such as quick lime, dolomite and iron ore. The charge is then refined through oxygen blowing so that it is converted to steel. Such a refining treatment is performed for about 17 minutes.
FIG. 1A illustrates the process of discharging the molten steel from the converter after the refining treatment. As shown in FIG. 1A, the converter 1 is tilted by a predetermined angle, and the molten steel 3 is poured off into a ladle 2 through a tapping hole 5 within about five minutes. As the pouring of the molten steel 3 should be performed free from slag, such a process is usually called the xe2x80x9cslag free tapping.xe2x80x9d
However, as shown in FIG. 1B, in the slag free tapping process, large sized vortex is formed at the molten steel 3 and the slag 4, and much of the slag 4 is carried over from the converter and flowed into the ladle 2 in addition to the molten steel 3. This makes bad effect to the cleanliness of the steel, and makes it difficult to control slag composition at the second refining process. Furthermore, large amount of deoxidizing agent should be additionally used to deoxidize the slag accompanied with the molten steel.
FIG. 2A illustrates a technique of blocking leakage of the carried over slag 4 from the converter 1 based on a large sized spherical slag check ball 7. As shown in FIG. 2B, the slag check ball 7 has a specific gravity higher than the slag 4, but lower than the molten steel 3. Therefore, when the molten steel 3 and the slag 4 are coexistent, the slag check ball 7 is constantly disposed between the molten steel 3 and the slag 4. That is, as shown in FIG. 20, the slag check ball 7 separates the slag 4 from the molten steel 3 during the slag free tapping process. However, the slag check ball 7 blocks the tapping hole 5 only when most of the molten steel is poured off. Practically, the slag check ball 7 is floating over the molten steel or rotated due to the influence of the vortex 6 during most of time for the slag free tapping process. Therefore, this technique cannot effectively block leakage of the carried over slag 4 due to the vortex 6.
Korean Patent Application Nos. 1991-24901 and 1992-9531 disclose another technique of blocking leakage of the carried over slag from the converter. In this technique, a gas blower is provided at the slag check ball charging equipment to blow gas onto the slag layer. When the gas is blown into the converter, naked molten steel becomes generated at the top side of the tapping hole, and the slag is thrust toward the periphery. However, in this technique, the slag check ball charging equipment with the gas blower should move forwards correctly at the tilting time of the converter, and after the tilting, the slag check ball charging equipment should again move backwards in a suitable manner. Furthermore, in such a structure, high pressure gas is liable to be blown into the converter so that the molten steel becomes turbulent, rather causing leakage of the slag. In addition, either a separate gas blower should be provided at the converter, or the existent slag check ball charging equipment should be re-made such that it has both of the capacities of charging the slag check ball and blowing gas into the converter. In short, the above technique involves complicated processing steps, making it difficult to be employed in practical application.
Alternatively, it has been suggested that a porous typed tapping hole may be used to blow gas into the converter. In this technique, the tapping hole is formed with a porous refractory material. A gas line is connected to the porous typed tapping hole, and gas is blown into the converter through the pores of the tapping hole. Therefore, the gas blown into the converter generates naked molten steel at the top side of the tapping hole, and forces the slag toward the periphery to thereby block leakage of the carried over slag. However, as the life cycle of the porous typed tapping hole is at best 2-5% compared to the main body of the converter, it should be frequently replaced by a new one. Furthermore, the porous typed tapping hole is liable to be eroded due to the blown gas. In addition, when the gas is blown into the converter through the porous typed tapping hole, the in-flowing speed of the gas is seriously less than the out-flowing speed of the molten steel so that the gas is rather forced toward the tapping hole, causing erosion of the tapping hole and delay in tapping time. In this situation, when the amount of gas increases to overcome such a problem, the tapping time becomes longer as much.
As described above, the conventional techniques of blocking leakage of the carried over slag at the slag free tapping process bear complicated processing steps, poor production efficiency, and other structural problems.
It is an object of the present invention to provide a converter which can effectively block leakage of the carried over slag during the slag free tapping process in a stable manner.
This and other objects may be achieved by a converter. The converter includes a side wall, and a tapping hole placed at the side wall to allow passage of molten steel. A refractory plug is axially spaced apart from the tapping hole with a predetermined distance. The distance between the refractory plug and the tapping hole is in the range of 3-5d where d indicates the inner diameter of the tapping hole. The refractory plug has one or more heat resisting steel tubes.
When the molten steel is discharged through the tapping hole of converter to the ladle, inert gas, for example nitrogen or argon gas, is introduced into the converter through the refractory plug with a small amount of flow rate to prevent leakage of carried over slag.